Longitudinally flexible expandable stent

ABSTRACT

An expandable stent comprises a multiplicity of sets of strut members. Each set of strut members forms a circumferentially extending closed structure with adjacent sets of strut members being coupled each to the other by connectors. The stent has two types of sets of strut members, a first type of set of strut members and a second type of set of strut members. The first type of set of strut members has a shorter total pathlength about the periphery of the stent than the second type of set of strut members. When the stent is radially deployed to its nominal diameter, the first type of set of strut members has greater radial rigidity as compared to the second type of set of strut members.

This application is a continuation of U.S. application Ser. No. 08/511,076, filed Aug. 3, 1995, now U.S. Pat. No. 6,818,014 which is a continuation-in-part of U.S. application Ser. No. 08/396,569, filed Mar. 1, 1995, now abandoned, the contents of both applications are incorporated herein in their entirety by reference.

This invention relates to an endoprosthesis device for implantation within a body vessel, typically a blood vessel. More specifically, it relates to a tubular expandable stent of improved longitudinal flexibility.

BACKGROUND OF THE INVENTION

Stents are placed or implanted within a blood vessel for treating stenoses, strictures or aneurysms therein. They are implanted to reinforce collapsing, partially occluded, weakened, or dilated sections of a blood vessel. They have also been implanted in the urinary tract and in bile ducts.

Typically, a stent will have an unexpanded (closed) diameter for placement and an expanded (opened) diameter after placement in the vessel or the duct. Some stents are self-expanding and some are expanded mechanically with radial outward force from within the stent, as by inflation of a balloon.

An example of the latter type is shown in U.S. Pat. No. 4,733,665 to Palmaz, which issued Mar. 29, 1988, and discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes an arrangement wherein a balloon inside the stent is inflated to expand the stent by plastically deforming it, after positioning it within a blood vessel.

A type of self-expanding stent is described in U.S. Pat. No. 4,503,569 to Dotter which issued Mar. 12, 1985, and discloses a shape memory stent which expands to an implanted configuration with a change in temperature. Other types of self-expanding stents not made of shape memory material are also known.

This invention is directed to stents of all these types when configured so as to be longitudinally flexible as described in detail hereinbelow. Flexibility is a desirable feature in a stent so as to conform to bends in a vessel. Such stents are known in the prior art. Examples are shown in U.S. Pat. No. 4,856,516 to Hillstead; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 4,994,071 to MacGregor; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,195,984 to Schatz; U.S. Pat. No. 5,135,536 to Hillstead; U.S. Pat. No. 5,354,309 to Shepp-Pesch et al.; EPO Patent Application 0 540 290 A2 to Lau; EPO Patent Application No. 0 364 787 B1 to Schatz, and PCT Application WO 94/17754 (also identified as German Patent Application 43 03 181).

Generally speaking, these kinds of stents are articulated and are usually formed of a plurality of aligned, expandable, relatively inflexible, circular segments which are interconnected by flexible elements to form a generally tubular body which is capable of a degree of articulation or bending. Unfortunately, a problem with such stents is that binding, overlapping or interference can occur between adjacent segments on the inside of a bend due to the segments moving toward each other and into contact or on the outside of a bend the segments can move away from each other, leaving large gaps. This can lead to improper vessel support, vessel trauma, flow disturbance, kinking, balloon burst during expansion, and difficult recross for devices to be installed through already implanted devices and to unsupported regions of vessel.

A diamond configuration with diagonal connections between each and every diamond of each segment is also known but such closed configurations lack flexibility.

It is an object of this invention to provide a longitudinally flexible stent of open configuration that avoids these problems and exhibits improved flexibility (radially and longitudinally) in the stent body segments thereof rather than in flexible joints between the segments.

SUMMARY OF THE INVENTION

To this end, the invention provides a tubular expandable stent, comprising: a plurality of cylindrical shaped open cylindrical segments aligned on a common longitudinal axis to define a generally tubular stent body, each segment being defined by a member formed in an undulating flexible pattern of interconnected substantially parallel struts with pairs thereof having alternating interconnecting end portions to define the periphery of the expandable stent segment, and in which the connected end portions of paired struts in each segment, before the stent is expanded, are positioned substantially opposite to connected end portions of paired struts in adjacent segments. The segments are interconnected by a plurality of interconnecting elements extending from some of the connected end portions on one segment to some of the connected end portions on adjacent segments in such a manner that there are three or more legs between points of connection from one side of each segment to its other side. Additionally, the connecting elements extend angularly from connecting end portion of one segment to connecting end portion of an adjacent segment, not to an opposite connecting end portion on an adjacent segment, whereby upon expansion of the stent the adjacent segments are displaced relative to each other about the periphery of the stent body to accommodate flexing of the stent within paired struts without interference between adjacent segments, rather than by means of articulating flexible connectors between segments. As a result, the connectors between the segments are not intended to flex or bend under normal use.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a flat view of an unexpanded stent configuration according to the invention.

FIG. 2 shows the pattern of FIG. 1 in a tubular, unexpanded stent.

FIG. 3 shows an expanded stent of the configuration shown in FIG. 1.

FIG. 4 shows a flat view of an alternate unexpanded stent configuration according to the invention.

BEST MODE DESCRIPTION OF THE INVENTION

Turning to the Figures, FIG. 1 and FIG. 2 show a fragmentary flat view of an unexpanded stent configuration and the actual tubular stent (unexpanded), respectively. That is, the stent is shown for clarity in FIG. 1 in the flat and may be made from a flat pattern 10 (FIG. 1) which is formed into a tubular shape by rolling the pattern so as to bring edges 12 and 14 together (FIG. 1). The edges may then be joined as by welding or the like to provide a configuration such as that shown in FIG. 2.

The configuration can be seen in these Figures to be made up of a plurality of adjacent segments generally indicated at 16, each of which is formed in an undulating flexible pattern of substantially parallel struts 18. Pairs of struts are interconnected at alternating end portions 19 a and 19 b. As is seen in FIG. 1, the interconnecting end portions 19 b of one segment are positioned opposite interconnecting end portions 19 a of adjacent segments. The end portions as shown are generally elliptical but may be rounded or square or pointed or the like. Any configuration of end portions is acceptable so long as it provides an undulating pattern, as shown. When the flat form 10 is formed into an unexpanded tube as shown in FIG. 2, the segments are cylindrical but the end portions 19 of adjacent segments remain in an opposed position relative to each other.

A more preferred method of manufacture begins with a thin walled tube which is then laser cut to provide the desired configuration. It may also be chemically etched or EDM'd (electrical discharge machined) to form an appropriate configuration.

Interconnecting elements 20 extend from one end portion 19 of one segment 16 to another end portion 19 of another adjacent segment 16 but not to an oppositely positioned end portion 19 of an adjacent segment 16. There are at least three struts included between the points on each side of a segment 16 at which an interconnecting element 20 contacts an end portion 19. This results in the interconnecting elements 20 extending in an angular direction between segments around the periphery of the tubular stent. Interconnecting elements 20 are preferably of the same length but may vary from one segment to the other. Also, the diagonal direction may reverse from one segment to another extending upwardly in one case and downwardly in another, although all connecting elements between any pair of segments are substantially parallel. FIG. 1, for example shows them extending downwardly, right to left. Upwardly would extend up left to right in this configuration.

As a result of this angular extension of the interconnecting elements 20 between adjacent segments and loops, upon expansion of the stent as seen in FIG. 3, the closest adjacent end portions 19 between segments 16 are displaced from each other and are no longer opposite each other so as to minimize the possibility of binding or overlapping between segments, i.e., pinching.

The number of interconnecting elements 20 may vary depending on circumstances in any particular instance. Three per segment are satisfactory for the configuration shown and at least three will be used typically.

The alternate design shown in FIG. 4 includes longer struts 18 a in the two end segments 16 a than in the intermediate segments 16. This allows the end segments (16 a) to have less compression resistance than the intermediate segments (16), providing a more gradual transition from the native vessel to the support structure of the stent. Otherwise, the configuration is the same as that shown in FIG. 1.

As already indicated, this invention is applicable to self-expanding configurations, mechanically expandable configurations and to a wide variety of materials, including both metal and plastic and any other material capable of functioning as an expandable stent. For example, the stent may be of metal wire or ribbon such as tantalum, stainless steel or the like. It may be thin-walled. It may be of shape memory alloy such as Nitinol or the like, etc.

The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto. 

1. A cylindrical stent formed from a single piece of metal, the stent comprising a multiplicity of sets of strut members with each set of strut members forming a closed cylindrical structure having a longitudinal axis collinear with a longitudinal axis of the stent, the closed structure comprised of interconnected strut members, each strut member connected at a first end to an adjacent strut member and at a second end to another adjacent strut member, in an expanded state of the stent each strut member being non-parallel to the longitudinal axis, adjacent closed cylindrical structures being coupled each to the other by connectors, each of said connectors being diagonal relative to the longitudinal axis, said stent having a proximal end, a distal end and a center section located approximately half-way between said proximal and distal ends, said stent having two types of circumferentially extending sets of strut members, a first type of set of strut members and a second type of set of strut members, the first type of set of strut members having a shorter total circumferential length as compared to the total circumferential length of the second type of set of strut members, only the set of strut members at the distal end of the stent and only the set of strut members at the proximal end of the stent being the second type of set of strut members, the stent when expanded having a uniform diameter and having the first type of set of strut members having greater radial rigidity as compared to the second type of set of strut members.
 2. The stent as recited in claim 1 where said first type of set of strut members has a length that is less than the length of said second type of set of strut members.
 3. The stent as recited in claim 1 where there is at least one of the first type of set of strut members at said center section of the stent.
 4. The stent as recited in claim 1 where said stent is balloon expandable.
 5. The stent as recited in claim 1 where said stent is a radially self-expanding stent.
 6. The stent as recited in claim 1 where said stent is a mechanically expandable stent.
 7. The stent of claim 1 wherein the connectors are disposed at an oblique angle relative to the longitudinal axis of the stent.
 8. A stent formed from a single piece of material, the stent comprising a multiplicity of sets of strut members with each set of strut members forming a serpentine closed cylindrical structure which forms a circumference of the stent, the closed structure comprised of strut members, each strut member connected at a first end to one adjacent strut via a curved end segment and at a second end to another adjacent strut via another curved end segment, the curved end segments being of the same length, adjacent closed cylindrical structures being coupled each to the other by connectors, each connector being diagonal relative to a longitudinal axis of the stent, said stent having a proximal end, a distal end and a center section located approximately half-way between said proximal and distal ends, said stent having two types of circumferentially extending sets of strut members, a first type of set of strut members and a second type of set of strut members, the first type of set of strut members forming a path that follows along the serpentine closed structure of one of the sets of strut members about the periphery of the stent which has a shorter total length as compared to the total length of a pathway that follows along the serpentine closed structure of another of the sets of strut members about the periphery of the stent formed by the second type of set of strut members, only the set of strut members at the distal end of the stent and only the set of strut members at the proximal end being the second type of set of strut members, the stent when expanded having a uniform diameter and having the first type of set of strut members having greater radial rigidity as compared to the second type of set of strut members.
 9. The stent of claim 8 wherein the connectors are disposed at an oblique angle relative to the longitudinal axis of the stent.
 10. The stent of claim 8 wherein the circumferentially extending closed structure is in the form of a cylindrical zig-zag. 